SimplifyCFG: Correctly handle switch lookup tables which fully cover the input type...

When using bit tests for hole checks, we call AddPredecessorToBlock to give the
phi node a value from the bit test block. This would break if we've
previously called removePredecessor on the default destination because the
switch is fully covered.

Test case by Mark Lacey.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@235771 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Transforms/Utils/SimplifyCFG.cpp b/lib/Transforms/Utils/SimplifyCFG.cpp
index 7c239cb19b70e0c2b73c0a75c85b1d01a1af9e24..60ac271bceb7099aae39129b1a9b433688dc404f 100644 (file)
--- a/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -4159,10 +4159,8 @@ static bool SwitchToLookupTable(SwitchInst *SI, IRBuilder<> &Builder,
 
   if (!DefaultIsReachable || GeneratingCoveredLookupTable) {
     Builder.CreateBr(LookupBB);
-    // We cached PHINodes in PHIs, to avoid accessing deleted PHINodes later,
-    // do not delete PHINodes here.
-    SI->getDefaultDest()->removePredecessor(SI->getParent(),
-                                            /*DontDeleteUselessPHIs=*/true);
+    // Note: We call removeProdecessor later since we need to be able to get the
+    // PHI value for the default case in case we're using a bit mask.
   } else {
     Value *Cmp = Builder.CreateICmpULT(TableIndex, ConstantInt::get(
                                        MinCaseVal->getType(), TableSize));
@@ -4214,6 +4212,13 @@ static bool SwitchToLookupTable(SwitchInst *SI, IRBuilder<> &Builder,
     AddPredecessorToBlock(SI->getDefaultDest(), MaskBB, SI->getParent());
   }
 
+  if (!DefaultIsReachable || GeneratingCoveredLookupTable) {
+    // We cached PHINodes in PHIs, to avoid accessing deleted PHINodes later,
+    // do not delete PHINodes here.
+    SI->getDefaultDest()->removePredecessor(SI->getParent(),
+                                            /*DontDeleteUselessPHIs=*/true);
+  }
+
   bool ReturnedEarly = false;
   for (size_t I = 0, E = PHIs.size(); I != E; ++I) {
     PHINode *PHI = PHIs[I];

diff --git a/test/Transforms/SimplifyCFG/X86/switch_to_lookup_table.ll b/test/Transforms/SimplifyCFG/X86/switch_to_lookup_table.ll
index cdc0488991a4356a6af88c1c8174a0fed0775534..732e7cafe5ee85ab1f19ac511247653051d78c72 100644 (file)
--- a/test/Transforms/SimplifyCFG/X86/switch_to_lookup_table.ll
+++ b/test/Transforms/SimplifyCFG/X86/switch_to_lookup_table.ll
@@ -1273,3 +1273,32 @@ end:
 ; CHECK-LABEL: @pr20210
 ; CHECK: switch i8 %x
 }
+
+; Make sure we do not crash due to trying to generate an unguarded
+; lookup (since i3 can only hold values in the range of explicit
+; values) and simultaneously trying to generate a branch to deal with
+; the fact that we have holes in the range.
+define i32 @covered_switch_with_bit_tests(i3) {
+entry:
+  switch i3 %0, label %l6 [
+    i3 -3, label %l5
+    i3 -4, label %l5
+    i3 3, label %l1
+    i3 2, label %l1
+  ]
+
+l1: br label %l2
+
+l2:
+  %x = phi i32 [ 1, %l1 ], [ 2, %l5 ]
+  br label %l6
+
+l5: br label %l2
+
+l6:
+  %r = phi i32 [ %x, %l2 ], [ 0, %entry ]
+  ret i32 %r
+; CHECK-LABEL: @covered_switch_with_bit_tests
+; CHECK: entry
+; CHECK-NEXT: switch
+}